The present invention relates to gas depolarized electrochemical power sources, such as metal-air batteries or fuel cells of the type that are supplied with reactive gas by an active air moving device, and more particularly relates to an air mover mechanism that utilizes a diaphragm or bellows to move air in and out of one or more air openings or to move air from an inlet to an outlet.
Generally described, a metal-air cell, such as a zinc-air cell, uses one or more air permeable cathodes separated from a metallic zinc anode by an aqueous electrolyte. During operation of the cell, oxygen from the ambient air is converted at the one or more cathodes to produce hydroxide ions. The metallic zinc anode is then oxidized by the hydroxide ions. Water and electrons are released in this electrochemical reaction to provide electrical power.
Initially, metal-air cells found limited commercial use in devices, such as hearing aids, which required a low level of power. In these cells, the air openings which admitted air to the air cathode were so small that the cells could operate for some time without flooding or drying out as a result of the typical difference between the outside relative humidity and the water vapor pressure within the cell. However, the power output of such cells was too low to operate devices such as camcorders, cellular phones, or laptop computers. Furthermore, enlarging the air openings of a typical xe2x80x9cbutton cellxe2x80x9d was not practical because it would lead to premature failure as a result of flooding or drying out.
In order to increase the power output of metal-air cells so that they could be used to operate devices such as camcorders, cellular phones, or laptop computers, air managers were developed with a view to providing a flow of reactive air to the air cathodes of one or more metal-air cells while isolating the cells from environmental air and humidity when no output is required. As compared to conventional electrochemical power sources, metal-air cells containing air managers provide relatively high power output and long lifetime with relatively low weight. These advantages are due in part to the fact that metal-air cells utilize oxygen from the ambient air as the reactant in the electrochemical process as opposed to a heavier material such as a metal or a metallic composition. Examples of air managers are shown in U.S. Pat. Nos. 4,913,983, 5,356,729, 5,691,074 and 5,919,582.
A disadvantage of most air managers, however, is that they utilize an air moving device, typically a fan or an air pump, that occupies space that could otherwise be used for battery chemistry to prolong the life of the battery. This loss of space presents a particular challenge in attempts to provide a practical metal-air cell in small enclosures such as the xe2x80x9cAAxe2x80x9d cylindrical size now used as a standard in many electronic devices.
In addition to being bulky, air moving devices used in metal-air batteries also consume energy stored in the metal-air cells that might otherwise be delivered as power output to a load. Complicated electronics for controlling an air manager can increase this use of stored energy; in addition they add considerable expense. Also, as most air moving devices used in metal-air cells distribute air to a cathode plenum at low pressure, a flow path must be defined passing over all regions of the cathode surface to evenly distribute air to the entire cathode surface. Thus, the function of bringing in make up air and the function of mixing and distributing air within the battery have been separate. A further disadvantage of fans used as air moving devices in metal-air cells is that they may create noise at a level disruptive to users of devices such as cellular telephones.
As a result, while a key advantage of metal-air cells is their high energy density resulting from the low weight of the air electrode, this advantage has been compromised by the cost, space and power required for an effective air manager, and the noise it may produce. In addition, the operation of the air manager may not be necessary for all levels of power draw from the metal-air cell.
Fuel cells of the type that provide a gaseous or liquid fuel, such as hydrogen or methanol, also may benefit from an air manager that can provide air at a gas depolarized electrode while maintaining a needed hydration level in an electrolyte or hydrated membrane (xe2x80x9cpolymer electrolytexe2x80x9d).
Therefore, there has been a need in the art for an air manager incorporating an air moving device that occupies less of the volume available for battery chemistry, is usable with advanced systems for isolating the air electrodes when power is not being drawn from the metal-air cell, is quiet, needs relatively simple controls, consumes power at a relatively low rate, and provides similar advantages for fuel cells. There is a further need for a control means for the air manager that operates the air manager when necessary during high current draw modes and causes the air manager not to operate during low current draw modes.
The present invention seeks to provide an improved gas moving device for gas depolarized cells that occupies a minimal amount of the volume available for other cell components, is usable with advanced systems for isolating the air electrodes when power is not being drawn from the cell, requires either simple or no control logic circuitry, is quiet, and consumes power at a relatively low rate.
In accordance with one aspect of the invention, this object is accomplished by placing the cell or battery of cells in a casing with at least one ventilation passageway extending from the gas electrodes to an outside gas supply. A resilient diaphragm is placed within the casing and caused to reciprocate, moving in one direction by an electrically induced force an electromagnetic field and in the opposite direction by the resiliency of the diaphragm. The movement of the diaphragm causes gas to be exchanged between the interior of the casing adjacent to the gas electrode and exterior of the casing through the ventilation passageway.
In a preferred embodiment, the present invention provides a resilient ferromagnetic diaphragm having two sides. A coil is positioned near the diaphragm in order to attract the resilient ferromagnetic diaphragm when an electromagnetic field is created by an electrical current passing through the coil. When the electrical current through the coil is switched off, the diaphragm returns to its original position due to the resiliency of the diaphragm. The resilient ferromagnetic diaphragm may be constructed of a resilient diaphragm with a ferromagnetic plate attached to one side or may be formed from a resilient ferromagnetic material.
In another embodiment, the present invention provides a resilient ferromagnetic diaphragm with two sides and a coil positioned near the diaphragm. An electrical circuit with an electrical current source is used to direct an electrical current through the coil. The current through the coil creates an electromagnetic magnetic field which attracts the diaphragm and causes it to move when a predetermined level of electrical current passes through the coil.
The electrical circuit also contains a pair of contacts with one of the contacts connected to the diaphragm. The contacts are closed when the current flow through the coil is less than a predetermined level. However, when the current flow through the coil is greater than a predetermined level, the diaphragm moves. As the diaphragm moves, the contacts are opened, thus breaking the circuit, de-energizing the coil, and allowing the resiliency of the diaphragm to return it to the original position and remaking the circuit. The de-energizing and re-energizing of the coil may be repeated to cause the diaphragm to oscillate. Also, the resilient ferromagnetic diaphragm may be constructed of a resilient diaphragm with a ferromagnetic plate attached to one side or may be formed from a resilient ferromagnetic material.
In yet another embodiment, the present invention provides an electrically activated diaphragm with two sides. An electrical circuit with an electrical current source is used to direct an electrical current through the electrically activated diaphragm. The current through the electrically activated diaphragm causes the diaphragm to deform when a predetermined level of electrical current passes through it.
The electrical circuit also contains a pair of contacts with one of the contacts connected to the diaphragm. The contacts are closed when the current flow through the electrically activated diaphragm is less than a predetermined level. However, when the current flow through the electrically activated diaphragm is greater than a predetermined level, the diaphragm deforms. As the diaphragm deforms, the contacts are opened, thus breaking the circuit, and allowing the diaphragm to return it to the original position and remaking the circuit. The de-energizing and re-energizing of the diaphragm may be repeated to cause the diaphragm to oscillate. Also, the electrically activated diaphragm may be constructed of a piezoelectric or EAPS material, or a resilient diaphragm with a strip of piezoelectric material attached to one side.
Another aspect of the invention is a method for moving air in gas depolarized cell or battery of cells by encasing the cell or battery of cells in a body having at least one ventilation passageway and reciprocating a resilient diaphragm contained in the body in one direction with an electromagnetic field and in the other direction by the resiliency of the diaphragm. By reciprocating the diaphragm, air adjacent to the air electrode is exchanged between the interior and exterior of the body. The gas depolarized cell may be either a metal-air cell or a fuel cell of the type that provide a gaseous or liquid fuel, such as hydrogen or methanol.
In a preferred embodiment, the resilient diaphragm is manipulated by positioning a coil near the diaphragm and moving the diaphragm when an electromagnetic field is created by an electrical current passing through the coil. When the electrical current through the coil is switched off, the diaphragm returns to its original position due to the resiliency of the diaphragm.
In another embodiment the manipulation of the diaphragm is controlled by positioning a coil in proximity to the resilient ferromagnetic diaphragm; providing an electrical circuit having an electrical current source; and directing electrical current from the electrical current source through the coil to create an electromagnetic magnetic field to attract the diaphragm and cause it to move when a predetermined level of electrical current passes through the coil. Next in this method the diaphragm is manipulated by providing a pair of contacts with one of the contacts connected to the diaphragm and closed when current flow through the coil is less than a predetermined level; and moving the diaphragm when the presence of current flow through the coil is greater than a predetermined level. When the diaphragm moves, the contacts open thus breaking the circuit, de-energizing the coil, and allowing the resiliency of the diaphragm to return it to the original position.
The electrical circuit may be reestablished when the contacts are closed after the diaphragm has returned to its original position. When this is done, the electromagnetic magnetic field is recreated and attracts the diaphragm, thus causing the oscillation of the diaphragm while the electrical current available to the coil is greater than a predetermined level.
Another aspect of the invention is an gas mover system for an gas depolarized power supply associated with a load having at least two modes of operation drawing different levels of current from the power supply. A casing having at least one ventilation passageway is utilized to contain one or more cells. The gas may be, for example, air containing oxygen. An air mover is positioned to move air from the exterior to the interior of the casing adjacent to an air electrode of the cell and from the interior adjacent to an air electrode of the cell to the exterior of the casing. The passageway permits a predetermined low flow rate of air from the exterior to the interior of the casing adjacent to an air electrode of the cell during a low current draw mode of operation while the air mover is inoperative. The air mover, however, becomes operative responsive to the initiation of a high current draw mode of operation in a preferred embodiment. In a preferred embodiment, a fan or a resilient reciprocating diaphragm may be used as the air mover and may be powered by the power supply.
The operation of the air mover may be determined by a controller which monitors the load on the power supply. This controller can determine if the load on the power supply corresponds to the high current draw mode of operation and operate the air mover if this condition is found. Also, the controller may be a current divider circuit designed to restrict current to an electric air pump to a magnitude sufficient not to operate the air pump during the low current draw mode and yet direct a magnitude of current to the air pump sufficient to operate during the high current draw mode. Such a circuit can operate on the breaking and remaking principle described above.
This system may be used, for example in a cellular telephone environment. The low current draw mode of the system can correspond to the stand-by mode of a cellular telephone and the high current draw mode of operation can correspond to the transmit/receive mode.
Another aspect of the invention is a method of admitting air to an gas depolarized power supply associated with a load having at least two modes of operation drawing different levels of current from the power supply.
In a preferred embodiment, this is accomplished by enclosing the power supply in a casing with at least one ventilation passageway extending through the casing; initiating the operation of an air mover responsive to the initiation of a high current draw mode of operation of the load on the power supply; and terminating the operation of the air mover during a low current draw mode of operation of the load. The ventilation passageway permits a predetermined low flow rate of air from the exterior to the interior of the casing while the air mover is inoperative.
The operation of the air mover may be determined by monitoring the load on the power supply; determining if the load corresponds to the high current draw mode of operation; and operating the air mover if the load corresponds to the high current draw mode of operation. Also, an electric air mover may be employed by restricting current to the electric air pump to a magnitude sufficient not to operate during the low current draw mode of operation and directing a magnitude of current to the electric air pump sufficient to operate during the high current draw mode of operation.
In addition, this method may be employed in a cellular telephone environment by utilizing the low current draw mode of operation during the stand-by mode of a cellular telephone and utilizing the high current draw mode of operation during the transmit/receive mode of the cellular telephone.
Yet another aspect of the invention is an air mover system for an gas depolarized cell or battery of cells where the cell or battery of cells is to provide energy for an electrical device. A casing removable from the electrical device is utilized to contain the cell or battery of cells. The casing contains at least one ventilation passageway extending through the casing that mates with the electronic device. A resilient diaphragm is placed within the electronic device and caused to reciprocate, moving in one direction by the force of an electromagnetic field and in the opposite direction by the resiliency of the diaphragm. The movement of the diaphragm causes air to be exchanged through the ventilation passageway thus moving air between the interior of the casing adjacent to the air electrode and exterior of the casing.
Other objects, features, and advantages of the present invention will become apparent upon reading the following description of exemplary embodiments, when taken in conjunction with the drawings and the claims.